The digital watermark technique is a technique to embed additional information into image data and voice data in away in which people do not recognize it. For example, when copyright information of content or purchase information of a user is embedded as a digital watermark, when the content is fraudulently leaked, it may be used for identifying the presence/absence of copyright information and the source of the leaking.
In addition, the digital watermark technique may also be applied to advertisement, other than the protection of content. For example, a video image to which information related to an item or a person featured in the video image (for example, Uniform Resource Locator (URL) information specifying the location where the information resource exists on the Internet) is distributed to a television set, a PC and the like. When the video image is displayed on the television set or the display device of the PC, the viewer captures the displayed image by a mobile terminal with a camera and the like, and detects the URL from the image using a dedicated application. Then, by operating the mobile terminal and accessing the Website at the location specified by the URL, it becomes possible for the viewer to instantly buy the item feature in the image, or to instantly obtain information of other works in which the person in the video image appears.
When a content to which such a digital watermark is embedded is subjected to a filter process, camera capturing and the like, the embedded digital watermark may be lost. For this reason, the digital watermark is required to be resistant to possible causes for the loss. However, enhancement of the intensity to embed the digital watermark in order to add such resistance causes image quality degradation as the original content is subjects to a greater change.
In relation to the technique to embed a digital watermark information into video data, a technique in which the brightness of each frame is changed cyclically based on digital watermark information has been known. In this technique, the light and dark of each frame changes in the time direction. This generates a difference in the brightness between the brightest frame and the darkest frame, which may be recognized as a flicker on the screen.
In addition, in relation to the digital watermark technique, a technique in which each frame of a video image is divided into a plurality of blocks, and information is embedded by combining signals of opposite phases into adjacent blocks.
In addition, a technique in which an N−1 dimension pattern is generated based on an embedding system generated based on embedding information, and an N dimension embedding pattern generated by modulating a periodic signal based on a value on the N−1 dimension pattern is superimposed into an input signal and output.
Meanwhile, techniques described in the following documents have been known.    Document 1: International Publication Pamphlet No. 2005/079072    Document 2: International Publication Pamphlet No. 2007/102403